Another day, another political sex scandal. This time, it's former California governor Arnold Schwarzenegger acknowledging this week that he fathered a child with a member of his household staff more than a decade ago.

And while psychologists and the public alike may not be surprised, we still wonder why he strayed. Experts say power gives men (and women) greater opportunity to stray and the overconfidence to think they'll get away with it.

Political sex scandals happen regularly and across the political spectrum, from former Democratic presidential hopeful John Edwards fathering a child with a former campaign worker to Republican governor of South Carolina Mark Sanford disappearing to "walk the Appalachian trail" with a woman he'd fallen for in Argentina. Cheating certainly happens among the nonpolitical as well, but research suggests that with power comes the temptation to stray — and many powerful men assume they'll get away with it.

"It's really been in the last 150 years that we have begun to hold men to a higher standard of fidelity," said Stephanie Coontz, a historian at The Evergreen State College in Washington and author of "Marriage, A History" (Viking Adult, 2005).

Before then, Coontz said, men were expected to cheat and women were expected to ignore it. For powerful men, that pattern of turning a blind eye continued through the 1960s.

"Powerful and rich men were expected to have mistresses, and the press just covered it up," Coontz told LiveScience. "So some of these guys are a little slow on the learning curve."

Power and temptation

Though men are almost always the perpetrators of U.S. political scandals, the urge to stray may be more tied to power than to gender. An upcoming study to be published in the journal Psychological Science finds that people with power are more likely to say they've cheated or indicate a desire to cheat than the average Joe. In a large, anonymous survey of 1,561 professionals, the researchers found that power is linked to confidence, and those with high confidence tend to stray. Among the powerful, gender seemed to make little difference in propensity to cheat, although with more men than women in positions of power, most adulterers were male. [Read: How To Tell If Your Partner Is Cheating]

It's hard to measure how many people in average, nonpolitical relationships cheat, because people are motivated to lie about infidelity even on anonymous surveys. One study presented in 2010 at the annual meeting of the American Sociological Association in Atlanta found that in a nationally representative survey, 3.8 percent of men and 1.4 percent of women indicated that they had been unfaithful. Higher earners of both genders were more likely to cheat.

Opportunities abound

The upcoming Psychological Science study did not find evidence that people who travelled more cheated more, but politicians do have more opportunities to stray than the average person.

"They do meet a lot of people," said Pepper Schwartz, a sociologist at the University of Washington in Seattle who studies sexuality and relationships. "Women are impressed with their position, and they are attractive to women who might have never noticed them if they were an accountant."

Indeed, Coontz said, gender role socialization plays right into the hands of potential political adulterers.

"There's a tremendous identification of power and privilege with sexual excitement, so it's easy for the guys to translate the ego trip they are on constantly into sexuality," Coontz said. Meanwhile, women who believe that rubbing elbows (or more) with the rich and powerful will benefit them are more likely to accept the position of mistress.

Gradually, Coontz said, the American public is becoming more indignant about news of politicians straying. But society is also quick to forgive, Coontz said, pointing out that former Speaker of the House Newt Gingrich feels free to run for president despite a history of adultery.

"We're expressing more indignation than people used to in the past, but it appears that as long as they do get married again and the current wife is supportive, we seem to give them another shot at it," Coontz said. "We still let powerful men off the hook much more easily than we let either women or less powerful men."